Re: [Valgrind-developers] adding system call support

[Bob F. <bfr...@si...>]

On Fri, 4 Jun 2004, Tom Hughes wrote:

>> The application code executed is:
>>
>>      struct sigevent event;
>>      memset( &event, 0, sizeof( struct sigevent ) );
>>      event.sigev_notify = SIGEV_THREAD;
>>      event.sigev_notify_function = &timer_thread_handler;
>>      event.sigev_value.sival_ptr = this;
>>      timer_create( CLOCK_REALTIME, &event, &timer_id );
>>
>> where timer_thread_handler is a function, and timer_id is part of the
>> enclosing C++ class.
>
> If timer_create is really a system call then how is that function
> getting invoked - does the kernel invoke it asynchronously like a
> signal handler? If so then addding support for that system is going
> to be non-trivial and won't be as simple as adding a wrapper for
> the call to vg_syscalls.c as you will have to teach valgrind how
> to catch and emulate the callback.

I agree that SIGEV_THREAD support requires some sort of participation 
from the thread library.  However as I mentioned before, the timer 
callback thread doesn't ever get invoked with this kernel & threads 
implementation.  To make matters more complicated, we are using the 
LFS threads implementation.  I do know that signal-based notification 
does work.

I'll go spelunking into the timer implementation to see how it works.

Bob
======================================
Bob Friesenhahn
bfr...@si...
http://www.simplesystems.org/users/bfriesen